1. Field of the Invention
This invention relates to a process cartridge and a developing-assembly unit which are used for electrophotographic image-forming apparatus, such as copying machines, printers and facsimile machines of any of full-color, monochrome and monochromatic color uses, having a mechanism in which a developer image(s) is/are formed on an electrostatic latent image bearing member and thereafter transferred onto a transfer material to form an image.
This invention also relates to a process cartridge and a developing-assembly unit which are used for full-color electrophotography to perform development by the use of non-magnetic one-component developers consisting of yellow, magenta, cyan and black developers.
2. Related Background Art
A number of methods are conventionally known as methods for electrophotography. In general, copies or prints are obtained by forming an electrostatic latent image on an image-bearing member (photosensitive member) by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a developer to form a developer image as a visible image, transferring the developer image to a transfer material such as paper, and then fixing the developer image to the transfer material by the action of heat and pressure or the like.
In recent years, such electrophotographic apparatus have been made compact because of the need for personal use of the apparatus. Meanwhile, there is an increasing demand for color-image formation. In particular, full-color image-forming apparatus must make use of a plurality of developing assemblies to form an image. In order to make such a full-color apparatus, it is required to design each developing assembly in a small size.
As conventional process cartridges, process cartridges for electrophotography are proposed which have various forms, such as a form in which a developer-holding container and an electrostatic latent image bearing member are integrally set, a form in which a developer-holding container and an electrostatic latent image bearing member are individually prepared and these are individually mounted to the apparatus to put them into use, and a form in which a developer-holding container is divided so that only a developer part can be replaced at the time of replenishment.
In particular, in the process cartridge in which the developer-holding container and the electrostatic latent image bearing member are integrally set, a large volume of a developer must be filled in a container of limited capacity because of various restrictions that developers be provided in a large volume and made to have a long lifetime and that the apparatus be made compact. Hence, such a process cartridge has a tendency that its developer-holding container has a complicated shape.
Accordingly, in order to make the image-forming apparatus compact, the shape of a developing assembly used for image formation is restricted by the layout of the apparatus main body. Because of such a restriction, process cartridges have employed various shapes. For example, a developer container is so designed as to be deep so that the developer can be held therein, as much as possible, at a limited position, or the space of the part holding the developer is partitioned to provide a plurality of holding chambers.
For example, Japanese Patent Application Laid-open No. 2001-42625 discloses an image-forming apparatus and a developing assembly which employ the combination of a developing assembly with a magnetic developer; the former consisting of a fist holding chamber for holding a developer and a second holding chamber communicating with the first holding chamber.
Meanwhile, even in process cartridges having developer-holding chambers having such a complicated shape, the developer must properly be circulated as in usual developing assemblies so that the developing performance can be made uniform throughout the initial development stage, the middle development stage and the last development stage. Accordingly, many studies have been made in order to make the developer circulate properly. For example, it is required to control the circulation of developer appropriately by the shape, agitation movement, and so forth, of an agitation means.
In addition, developing assemblies are being made adaptable to color-image formation. In order for them to be adaptable to color-image formation, not only a monochrome developer cartridge, but also developing assemblies having other color developers must be provided.
It is also highly demanded to form color images at a high speed. Accordingly, in order to meet such a demand, an in-line type full-color machine 110 has been developed in which yellow, magenta, cyan and black, developing assemblies are disposed on a straight line. In order to dispose the developing assemblies in such a way and achieve miniaturization of the assemblies and also hold therein the developers in large volumes, the cartridges must be thin and ensure a capacity for holding the developers.
In process cartridges thus made thin and made to have a large capacity, agitation and transport means tend to have a complicated construction. Accordingly, they are each so constructed as to have a plurality of rotary agitation and transport means. Since a plurality of such rotary agitation and transport means for the developer are provided, faulty transfer due to insufficient agitation of the developer tends to occur, compared with the case of a simple developer-transport means. Many studies on such agitation means have been made in terms of processes and mechanisms, and many devices have been produced. Consequently, however, apparatus have tended to become expensive because of a rise in the developing-assembly cost and the main-body cost incidental to the agitation. Also, especially in a developing system making use of non-magnetic one-component contact development, the bulk density of a developer therefor differs greatly from that of a magnetic toner, and hence the developer tends to be insufficiently agitated especially in the event the developer contains air. For this reason, with regard to the agitation of developers having a low bulk density like those of a non-magnetic one-component type, a specific method has been provided with respect to the relationship between the developer-holding part and the developer-transport means. Thus, any optimum circulation means has not been elucidated.
Meanwhile, as the developer, since it is used in the process cartridge having the developer-holding chamber having such a complicated shape, it is required to be a material whose fluidity, adherence and agglomeration have been controlled and which may hardly cause faulty circulation. Due to the structural restriction on the developing assembly as stated above, the developer may preferably be one having optimum physical properties. It is considered preferable that the physical properties required here are practical physical properties which more closely reflect the phenomena occurring in an actual developing assembly than measured values obtained from experimental results. The state in which the developer is actually used in the developing assembly is a condition in which the developer itself contains air to a certain extent. Such a condition differs from any condition in which, e.g., the degree of agglomeration of a developer is usually measured in an ideal-model condition, and hence it is not related to how the developer behaves actually in the developing assembly. In particular, the non-magnetic one-component developer is more greatly influenced by the bulk density of the developer than any magnetic developer or two-component developer, and the condition in which the developer is kept standing still differs greatly from its condition immediately after agitation. Accordingly, it is required to grasp the real fluidity, adherence and agglomeration of the non-magnetic one-component developer in the developing assembly, and to control these appropriately.
With regard to the fluidity characteristics of powders, a description relating to the floodability index advocated by Carr et al. is found in “Measurement of Physical Properties of Powders” (Asakura Shoten, 1963). This is an index expressing the fluidity at the time a powder contains air, and is a characteristic value used by showing the adherence, agglomeration, fluidity and so forth in marks.
This floodability index is also applied in electrophotographic developers. For example, Japanese Patent Application Laid-open No. 4-145755 discloses a one-component developer having a floodability index of from 50 to 80 and a developing system using the same. It discloses an effect that the use of the developer having such a floodability index can make the developer well transportable by agitation in the interior of the developing assembly. However, the above publication does not mention any relationship between the above developer and the developer-holding chamber, and does not suggest how the developer behaves when the developing assembly has a complicated and deep shape.
From the viewpoint of economical advantages, too, it is preferable that the developer remaining in a process cartridge having finished its service life is in a smaller quantity, and, in the developer-holding chamber having a complicated shape as stated above, it is necessary to use the developer with improved efficiency. For that reason, too, a synergistic effect is required which is attributable to the combination of the shape of the developer-holding chamber, the developer agitation means and the developer.